TY - JOUR

T1 - Optical photometry of two transitional millisecond pulsars in the radio pulsar state

AU - Stringer, J. G.

AU - Breton, R. P.

AU - Clark, C. J.

AU - Voisin, G.

AU - Kennedy, M. R.

AU - Mata Sánchez, D.

AU - Shahbaz, T.

AU - Dhillon, V. S.

AU - Van Kerkwijk, M.

AU - Marsh, T. R.

N1 - Funding Information: JGS, RPB, CJC,GV,MRK, and DMS acknowledge the support of the European Research Council, under the European Union's Horizon 2020 research and innovation program (grant agreementNo. 715051; Spiders). VSD and TM acknowledge the support of the Science and Technology Facilities Council (STFC), grant number ST/T000406/1.

PY - 2021/10

Y1 - 2021/10

N2 - We present ULTRACAM multiband optical photometry of two transitional millisecond pulsars (tMSPs), PSR J1023+0038 and PSR J1227-4853, taken while both were in their radio pulsar states. The light curves show significant asymmetry about the flux maxima in all observed bands, suggesting an asymmetric source of heating in the system. We model the light curves using the icarus binary code, using models with an additional `hotspot' heating contribution and an anisotropic heat redistribution model to treat the asymmetry. Our modelling reveals companion stars with underfilled Roche lobes in both PSRs J1023+0038 and J1227-4853, with Roche lobe filling factors in the range f similar to 0.82-0.92. While the volume-averaged filling factors are closer to unity, significant underfilling is unexpected from tMSPs as they must rapidly overfill their Roche lobes to start transferring mass, which occurs on time-scale of weeks or months. We discuss the motivation and validity of our extensions to the models and the implications of the underfilled Roche lobe, and suggest future work to further investigate the role of the filling factor in the tMSP cycle.

AB - We present ULTRACAM multiband optical photometry of two transitional millisecond pulsars (tMSPs), PSR J1023+0038 and PSR J1227-4853, taken while both were in their radio pulsar states. The light curves show significant asymmetry about the flux maxima in all observed bands, suggesting an asymmetric source of heating in the system. We model the light curves using the icarus binary code, using models with an additional `hotspot' heating contribution and an anisotropic heat redistribution model to treat the asymmetry. Our modelling reveals companion stars with underfilled Roche lobes in both PSRs J1023+0038 and J1227-4853, with Roche lobe filling factors in the range f similar to 0.82-0.92. While the volume-averaged filling factors are closer to unity, significant underfilling is unexpected from tMSPs as they must rapidly overfill their Roche lobes to start transferring mass, which occurs on time-scale of weeks or months. We discuss the motivation and validity of our extensions to the models and the implications of the underfilled Roche lobe, and suggest future work to further investigate the role of the filling factor in the tMSP cycle.

KW - binaries: close

KW - stars: evolution

KW - stars: neutron

KW - pulsars: individual: PSR J1023+0038

KW - pulsars: individual: PSR J1227-4853

UR - http://www.scopus.com/inward/record.url?scp=85116580518&partnerID=8YFLogxK

U2 - 10.48550/arXiv.2107.11306

DO - 10.48550/arXiv.2107.11306

M3 - Article

VL - 507

SP - 2174

EP - 2191

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

SN - 0035-8711

IS - 2

ER -